Field of the Invention
The field of the invention is data processing, or, more specifically, methods, apparatus, and products for migrating DMA mappings.
Description of Related Art
A logical partition may be configured to utilize a physical, rather than virtual, I/O adapter. Such a configuration may rely on direct memory access operations between the I/O adapter. In current server-class systems there are large I/O fabrics incorporating many layers of bridge chips, switches, and I/O devices. The I/O devices themselves may be further virtualized in technologies such as SR-IOV. DMA requests generated by an I/O device must properly access only the appropriate memory for the owning logical partition (LPAR) for that I/O device.
The mapping of DMA addresses to LPAR memory involves an I/O translation table and associated hardware, often called an I/O Memory Management Unit (IO MMU) with the particular mappings of physical memory to PCI DMA addresses known as Translation Control Entries (TCEs). Setting up the TCE tables involves both hardware configuration and software configuration across many layers of the system including the hypervisor and the logical partition. The logical partition calls to the hypervisor to map LPAR memory pages to a DMA address, and can then inform the I/O adapter of the DMA address or addresses that the I/O adapter can use for operation. Any changes to these relationships require the updated configuration mappings to be communicated across all parties. This limits both configuration flexibility and the ability to reconfigure (for example, due to hardware failure or resource movement).